1. Field of the Invention
This invention relates to a scanning device using a deflector rotating or rotatively vibrating at high speed, and more particularly to a scanning device suited for scanning a scanned surface in a slit-like fashion.
2. Description of the Prior Art
In scanning a flat scanned surface by the use of a deflector which is rotating or rotatively vibrating, there has been a difficulty that the length of the light path between the deflector and the scanned surface varies with rotation of the deflector. Therefore, in a device incorporating such a scanning system, it is necessary to correct the variation in the length of the light path by some means. In FIG. 1 of the accompanying drawings which schematically shows an example of the copying optical system incorporating such a scanning device, a scanned surface 1 forms a cylindrical plane centered at the axis of rotation 2 of a rotatable mirror 3. Thus, the light beam from the scanned surface 1 is deflected by the rotatable mirror 3 and when the light beam reaches a recording drum 5 through an image forming lens system 4, the length of the light path between the scanned surface and the recording drum 5 is always maintained constant irrespective of the angle of rotation of the rotatable mirror 3. However, such use of a cylindrical surface as the scanned surface not only involves the difficulty of making a large cylindrical surface but also encounters the inability to scan a flat scanned object.